Spend a Day With the World’s Only Grass-Eating Monkeys

Geladas, one of the flagship species of Africa’s alpine grasslands, are found only in the Ethiopian Highlands. They are the smallest vestige of a genus that millions of years ago stretched from South Africa to Spain and into India. Once among the most prominent primates—one species was the size of a gorilla—they were likely driven to extinction by climate changes, competition with more adaptable baboons, and our ancestors, who butchered them. Today all that remains of Theropithecus are geladas, which offer valuable, if imperfect, insight into the world inhabited by our predecessors. There is no other animal like them. Geladas’ most recognizable features are crimson patches of hairless skin on their chests. In females, this region changes color, and tiny sacs around its edge fill with fluid, often indicating that they are ready to mate. The pink on dominant males darkens to red. Other primates signal sexual readiness with their rumps, but these monkeys spend most of the day scooting on their rears, gorging. Most primates climb trees to eat fruit and leaves. Geladas use opposable thumbs to pluck grass blades and herbs. Like zebras, they mince food with their molars.

Guassa researchers, from Ethiopia and abroad, have followed the minutiae of the daily life of almost 500 individuals. They monitor activity, study relationships, track births, and document deaths. Yet much about geladas remains unknown. After a revolt in Ethiopia ousted Emperor Haile Selassie in 1974, a civil war made fieldwork difficult. In the early 1990s uprisings drove out the ruling communist junta, the Derg, and scientists returned. Today it’s still not clear how many geladas are left.

Spend a Day With the World’s Only Grass-Eating Monkeys

Geladas, one of the flagship species of Africa’s alpine grasslands, are found only in the Ethiopian Highlands. They are the smallest vestige of a genus that millions of years ago stretched from South Africa to Spain and into India. Once among the most prominent primates—one species was the size of a gorilla—they were likely driven to extinction by climate changes, competition with more adaptable baboons, and our ancestors, who butchered them. Today all that remains of Theropithecus are geladas, which offer valuable, if imperfect, insight into the world inhabited by our predecessors. There is no other animal like them. Geladas’ most recognizable features are crimson patches of hairless skin on their chests. In females, this region changes color, and tiny sacs around its edge fill with fluid, often indicating that they are ready to mate. The pink on dominant males darkens to red. Other primates signal sexual readiness with their rumps, but these monkeys spend most of the day scooting on their rears, gorging. Most primates climb trees to eat fruit and leaves. Geladas use opposable thumbs to pluck grass blades and herbs. Like zebras, they mince food with their molars.

Guassa researchers, from Ethiopia and abroad, have followed the minutiae of the daily life of almost 500 individuals. They monitor activity, study relationships, track births, and document deaths. Yet much about geladas remains unknown. After a revolt in Ethiopia ousted Emperor Haile Selassie in 1974, a civil war made fieldwork difficult. In the early 1990s uprisings drove out the ruling communist junta, the Derg, and scientists returned. Today it’s still not clear how many geladas are left.